Sugar transport and metabolism by Streptococcus mutans is directly related to the onset and formation of human dental caries (tooth decay). In S. mutans, sugar substrates are taken up by ABC transporters (e.g., the maltose transport and multiple sugar metabolism transport (MSM) systems), by specific permeases, and most commonly by phosphoenolpyruvate (PEP)-sugar phosphotransferase systems (PTS). To better understand this important dental pathogen, we have sequenced the entire DNA sequence of the genome of strain UA159 at the University of Oklahoma. Detailed computational analyses of the S. mutans genome showed the presence of five ABC transporters and fourteen PTS systems for the probable transport of sugars or sugar alcohols including glucose, sucrose, maltose, lactose and fructose. Since the uptake and metabolism of carbohydrates is the key step in the formation and release of cariogenic acid, and since completion of the genomic DNA sequence of S. mutans strain UA159 now permits us to locate all of the predicted coding regions, this proposed work will examine the global gene response in S. mutans. Additionally, because S. mutans grows in a plaque that is a natural biofilm, it is crucial to determine the alterations in gene expression in biofilm cultures. Therefore, the specific aims of this proposal are to 1) analyze the differences in global gene expression observed when S. mutans UA159 is grown in the presence of the most common dietary sugars (sucrose, maltose, lactose, glucose, and fructose) in planktonic culture and in biofilm, and 2) identify multiple transporters for the same sugar (as well as genes influenced by transport systems) in S. mutans planktonic and biofilm cultures by individually inactivating those systems. We hypothesize that many genes will have differential patterns of expression in response to the availability of carbohydrate source and culture state. The information obtained from the proposed study should dramatically advance our understanding of this important human pathogen and facilitate new approaches for treatment and intervention aimed at reducing the incidence of dental caries.